Indian Ocean circulation and productivity during the last glacial cycle (original) (raw)
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Glacial to Holocene changes in the surface and deep waters of the northeast Indian Ocean
Marine Geology, 2012
Stable carbon and oxygen isotopic investigations are carried out on planktonic and benthic foraminifera from an AMS-dated sediment core of the northeast Indian Ocean (NEIO) to infer glacial to Holocene changes in surface and deep waters. The chronology of this gravity core (SK157-14; water-depth 3306 m; lat. 5°11'N; long. 90°05'E) was established using six AMS radiocarbon ages and oxygen isotope stratigraphy. Variations in δ18O and δ13C values of planktonic (Globigerinoides ruber) and benthic foraminifera (Cibicidoides spp.) are suggestive of large changes in the surface and deep water characteristics during the last ~ 60 ka. The δ18Opl values in core SK157-14 are significantly higher compared to the sediment cores in the northern Bay of Bengal and the Andaman Sea because of the diminished influence of riverine fresh water fluxes. Large variations in planktonic δ18Opl are noticed during the Marine Isotopic Stage (MIS) 3.1 and 3.3. Glacial to Holocene Δδ18Opl amplitude (1.8‰) is consistent with other published oxygen isotope records from the nearby locations. Maximum enrichment in δ18Opl occurs at 24-19 and the minimum during 7-6 ka BP. Spectral analysis of planktonic δ18Opl time series suggests a teleconnection between surface water δ18O and North Atlantic climate oscillations. Benthic foraminiferal δ18Oben values indicate deep water cooling of ~ 1.5 °C during the last glacial maximum. The δ13Cben values are generally higher for the Holocene foraminifera suggesting greater contribution from the North Atlantic Deep Water (NADW). However glacial benthic foraminifera are characterized by lower δ13Cben values. Highly depleted δ13Cben values during the ~ 60-50, 21-17 and 13-11 ka BP intervals suggest decrease contribution from the North Atlantic Deep Water (NADW) and increase influx from the Southern Ocean Deep Water (SODW). In addition, oxidation of organic matter and ageing of the deep water may have contributed in the pronounced decrease in δ13Cben during the glacial intervals.
Palaeogeography, Palaeoclimatology, Palaeoecology, 1999
Palaeoceanographic conditions in the eastern Indian Ocean for the last ∼30 kyr are documented by means of planktonic foraminiferal analyses of 10 gravity cores. Quantitative foraminiferal analysis (%), Q-mode factor analysis, the modern analog technique (MAT) and oxygen-isotope analyses are used. A conspicuous increase during the last glacial maximum (LGM) of foraminiferal fragmentation resulting from a more productive Java upwelling system and/or a more corrosive Antarctic Intermediate Water (AAIW) was found at intermediate water depths (∼1000 m). Contrasting Q-mode factors based on foraminifera between today and the LGM suggest changes in the thermocline depth, sea-surface temperature (SST), upwelling, and the strength of both the Australasian Mediterranean Water (AAMW) and the Indian Central Water (ICW). The decrease in the percentage abundance of shallow-dwelling and symbiont-bearing planktonic foraminifera, the increase in percentage of the upwelling-related species Globorotalia cultrata and Neogloboquadrina dutertrei, and factor 3 (dominated by Globorotalia tumida and Globigerinella siphonifera) suggest a stronger Java upwelling system during the LGM. A steeper, steric latitudinal gradient (in the presence of a weak Leeuwin Current), and a geostrophic flow similar to today's is postulated for the LGM, and this must have prevented upwelling offshore Western Australia. Today's AAMW–ICW sharp front was weaker during the LGM when the AAMW was saltier, cooler, and nutrient richer and more similar to the ICW. During the LGM, a more gentle SST latitudinal gradient over the ∼16 to ∼23°S region contrasts with today's steeper conditions at the AAMW–ICW Front. Also, for the LGM, a nutrient-rich ICW may explain previously documented increases in mass accumulation rates of CaCO3, organic carbon and benthonic foraminifera in a region where the nutricline was deep and within the lower euphotic zone.
Journal of Asian Earth Sciences, 2006
This study attempts to analyse paleoceanographic changes in the Central Indian Ocean (Deep Sea Drilling Project Site 237), linked to monsoon variability as well as deep-sea circulation during the Plio-Pleistocene. We used factor and cluster analyses of census data of the 34 most dominant species of benthic foraminifera that enabled us to identify five biofacies: Astrononion umbilicatulum-Uvigerina proboscidea (Au-Up), Pullenia bulloides-Bulimina striata (Pb-Bs), Globocassidulina tumida-Nuttallides umbonifera (Gt-Nu), Gyroidinoides nitidula-Cibicides wuellerstorfi (Gn-Cw) and Cassidulina carinata-Cassidulina laevigata (Cc-Cl) biofacies. Knowledge of the environmental preferences of modern deep-sea benthic foraminifera helped to interpret the results of factor and cluster analyses in combination with oxygen and carbon isotope values. The biofacies indicative of high surface productivity, resulting from a stronger South Equatorial Current (Au-Up and Pb-Bs biofacies), dominate the early Pliocene interval (5.6-4.5 Ma) of global warmth. An intense Indo-Pacific 'biogenic bloom' and strong Oxygen Minimum Zone extended to intermediate depths (w1000-2000 m) over large parts of the Indian Ocean in the early Pliocene. Since 4.5 Ma, the food supply in the Central Indian Ocean dropped and fluctuated while deep waters were corrosive (biofacies Gt-Nu, Gn-Cw). The Pleistocene interval is characterized by an intermediate flux of organic matter (Cc-Cl biofacies). q
Journal of Asian Earth Sciences, 2019
Here we present the first detailed planktonic and benthic 13 C records and benthic foraminiferal assemblage records from the northeastern Indian Ocean to decipher the palaeoceanographic changes during the last 56 kyr. We identified three different palaeoceanographic stages, clearly differentiated by significant variations in the benthic foraminiferal assemblages and 13 C records. The results of this study indicate that productivity was generally higher during the glacial periods than during the Holocene. Comparison of the benthic foraminiferal assemblage distributions and planktonic and benthic 13 C records show a significant correlation between productivity and the bottom water oxygenation on glacial-interglacial timescales. Productivity gradually increased during the period between 56-27.5 kyr. During this period, the dominance of Melonis spp. and Oridosalis umbonatus were correlated with conditions of intermediate to high surface productivity and moderate bottom water oxygenation. Increased higher equatorial productivity and low bottom water oxygenation during the period between 27.5-15 kyr are supported by planktonic 13 C and faunal records. During this period, the dominance of benthic foraminifera assemblages characterised by Uvigerina peregrina indicates sustained continuous phytodetritus flux to the seafloor from enhanced surface water productivity and relatively low bottom water oxygenation. The absence or minimal occurrences of high productivity indicating U. peregrina, the dominance of intermediate to low productivity indicating fauna, and relatively low planktonic 13 C records suggest low productivity and active deep-water oxygenation after 15 kyr. Concurrent river discharge and rising sea levels during this period are indicated by negative 18 O of G. ruber at the site.
2005
Carbon-isotopes (δ 13 C) composition of benthic foraminifera has been extensively used to understand the link between deep-water circulation and climate. Equatorial Indian Ocean δ 13 C records of planktic- and benthic-foraminifera together show an unexplained shift in the long-term mean oceanic-δ 13 C around the penultimate glacial termination (T2: 132 ka). The time-series planktic- and benthic- species δ 13 C records exhibit two distinct mean-δ 13 C levels. The low mean-δ 13 C characterises the pre-T2 period (250 ka – 132 ka), while the post-T2 (~95 ka – Present) period records high mean-δ 13 C, generating a one-time shift of ~0.4 ‰ within the last ~250 kyr time-period. This shift is a result of consistently higher-δ 13 C in post-T2 glacial (and interglacial) periods as compared to the pre-T2 glacial (and interglacial) periods, and begins around the T2 (~132 ka), lasts until ~95 ka, and sustained through the T1. The normally observed glacial-interglacial δ 13 C variations of ~0.3 ‰...
Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records
Quaternary Science Reviews, 2002
We show that robust regressions can be established between relative sea-level (RSL) data and benthic foraminifera oxygen isotopic ratios from the North Atlantic and Equatorial Pacific Ocean over the last climatic cycle. We then apply these regressions to long benthic isotopic records retrieved at one North Atlantic and one Equatorial Pacific site to build a composite RSL curve, as well as the associated confidence interval, over the last four climatic cycles. Our proposed reconstruction of RSL is in good agreement with the sparse RSL data available prior to the last climatic cycle. We compute bottom water temperature changes at the two sites and at one Southern Indian Ocean site, taking into account potential variations in North Atlantic local deep water d 18 O. Our results indicate that a Last Glacial Maximum (LGM) enrichment of the ocean mean oxygen isotopic ratio of 0.95% is the lowest value compatible with unfrozen deep waters in the Southern Indian Ocean if local deep water d 18 O did not increase during glacials with respect to present. Such a value of the LGM mean ocean isotopic enrichment would impose a maximum decrease in local bottom water d 18 O at the North Atlantic site of 0.30% during glacials. r
Paleoceanography, 2015
Changes in ocean circulation structure, together with biological cycling, have been proposed for trapping carbon in the deep ocean during glacial periods of the Late Pleistocene, but uncertainty remains in the nature and timing of deep ocean circulation changes through glacial cycles. In this study, we use neodymium (Nd) and carbon isotopes from a deep Indian Ocean sediment core to reconstruct water mass mixing and carbon cycling in Circumpolar Deep Water over the past 250 thousand years, a period encompassing two full glacial cycles and including a range of orbital forcing. Building on recent studies, we use reductive sediment leaching supported by measurements on isolated phases (foraminifera and fish teeth) in order to obtain a robust seawater Nd isotope reconstruction. Neodymium isotopes record a changing North Atlantic Deep Water (NADW) component in the deep Indian Ocean that bears a striking resemblance to Northern Hemisphere climate records. In particular, we identify both an approximately in-phase link to Northern Hemisphere summer insolation in the precession band and a longer-term reduction of NADW contributions over the course of glacial cycles. The orbital timescale changes may record the influence of insolation forcing, for example via NADW temperature and/or Antarctic sea ice extent, on deep stratification and mixing in the Southern Ocean, leading to isolation of the global deep oceans from an NADW source during times of low Northern Hemisphere summer insolation. That evidence could support an active role for changing deep ocean circulation in carbon storage during glacial inceptions. However, mid-depth water mass mixing and deep ocean carbon storage were largely decoupled within glacial periods, and a return to an interglacial-like circulation state during marine isotope stage (MIS) 6.5 was accompanied by only minor changes in atmospheric CO 2. Although a gradual reduction of NADW export through glacial periods may have produced slow climate feedbacks linked to the growth of Northern Hemisphere ice sheets, carbon cycling in the glacial ocean was instead more strongly linked to Southern Ocean processes. Evidence on past Atlantic Ocean circulation derived from carbon isotope reconstructions has been used to suggest that ocean circulation is primarily responding to, rather than driving, Pleistocene climate change on orbital timescales. For example, Imbrie et al. [1992] placed deep Atlantic ventilation within a "late response" group of variables, with increased ventilation occurring~8 kyr behind precessional maxima in Northern Hemisphere insolation. More recently, Lisiecki et al. [2008] similarly proposed a lag of 6-11 kyr WILSON ET AL.
Reconstruction of palaeoproductivity from Southern Ocean is crucial for understanding the functioning of the Southern Ocean biological pump in the past. High resolution records of multi-proxy parameters (calcium carbonate, opal, total organic carbon biogenic barium and planktonic carbon isotope ratios (δ13C)) were investigated in two well-dated sediment cores (SK200/22a and SK200/27) from the Indian sector of Southern Ocean situated to the north and south of Antarctic Polar front (APF), respectively. The palaeoproductivity records extending 95 ka BP (SK200/22a) and 75 ka BP (SK200/27) revealed inverse relationships between the calcite and opal productivity, indicating the influence of shifting nutrient regimes. At core SK200/22a, reduced calcite productivity during marine isotope stage (MIS) 2, 4, and part of MIS 3 suggest an equatorward migration of the frontal regimes during glacial intervals. Compared to this, the region south of the APF (core SK200/27) was characterized by the near absence of calcite content during the last glacial period and increased opal productivity during MIS 1 and MIS 3, supporting a southward migration of APF during warmer intervals. Ba(bio) records exhibit good correlation with opal records in both the cores and also correlate with that of calcite record at SK200/ 22a, indicating that Ba is influenced by the combined opal and calcite productivity. The enhanced opal productivity during the glacial periods north of the APF is attributed to the northward shifting of oceanic fronts and associated transfer of nutrients. Diatom productivity records of SK200/22a reveal significant similarities with the dust records from the Antarctic and Southern Ocean, but showed no significant relationships with the diatom record of SK200/27. It is proposed that the dust-derived Fe input had apparently influenced the palaeoproductivity north of the modern APF, but had a minor influence on opal productivity south of the APF. Comparison with the ice core climate records from Antarctica and Greenland revealed that bioproductivity peaks in the study region are nearly synchronous with the millennial Antarctic warming events. Remarkably, the calcite and opal productivity records at SK200/22a responded differently to the Antarctic warming events, with opal productivity lagging behind the calcite productivity peaks by 1–2 ka.
Carbon isotopes in deep-sea benthic foraminifera: Precession and changes in low-latitude biomass
Geophysical Monograph Series, 2013
Detailed carbon isotope records have water enriched in i•C into the deep North Atlantic been obtained from benthic foraminifera in the during glacial periods alters the carbon isotopic North Atlantic (CHN 82 Sta 24 Core 4PC, 42øN, 32øW, signal of Atlantic cores relative to the global 3427 m, 244 kyr) and central equatorial Pacific mean [Streeter and Shackleton, 1979; Duplessy et (KNR 73 Sta 4 Core 3PC, OøS, 106øW, 3606 m, 410 al., 1975; Boyle and Keigwin, 1982; Curry and kyr). These data demonstrate that the North Lohmann, 1983; Shackleton et al., 1983; Berger and Atlantic site has always been nutrient depleted Keir, 1984]. The change in the oceanic average relative to the Pacific site. Although down-core carbon isotopic composition between the present and carbon isotope data in the Atlantic and Pacific the 18-kyr (1 kyr=103 years) glacial maximum is now reflect changes in dee?_-ocean circulation patterns, thought to be about 0.4•/o• [Shackleton et al., a larger fraction of •-SC variability in both 1983; E.A. Boyle and L.D. Keigwin, unpublished oceans is due to changes in the inventory of manuscr$•t, 1984], corresponding to a mass of about continental reduced carbon. The magnitude of this 50 x 10-moles of reduced carbon, about carbon isotope biomass signal is nearly twice as one-quarter of the present-day mass of carbon large during oxygen isotope stages 4 and 6 as it is stored in plants and soils. during stage 2. Carbon isotope variability in both The carbon isotopic records of Shackleton [1977] oceans contains significant power at the 23-kyr and Shackleton et al., [1983 I only covered the last frequency band which is coherent with insolation 140,000 years, so it was not possible from these changes caused by precession of the earth's data to determine if this same pattern of change rotational axis. We propose that this correlation has occurred over several glacial/interglacial is due to orbitally driven variations in transitions. In addition, the North Atlantic low-latitude biomass, and that the lower amplitude record is based on analysis of three species and of the carbon isotope signal during the last 60 kyr core M12392 is located in the eastern basin of the is due to the reduction in precession parameter amplitude during this period. Introduction Shackleton [ 1977] proposed that the carbon isotope composition of deep-sea benthic foraminifera changes in response to variations in the storage of carbon enriched in 13C in the trees and soils on the continents. He argued that destruction of the northern hardwood forests (by tropical Atlantic Ocean, which has been shown to have an anomalously large component due to ocean circulation changes l Curry and Lohmann, 1983]. In order to examine the variability of deep-sea carbon isotopic composition over time, we have obtained two benthic carbon isotope records from the western North Atlantic Ocean (over the last 244,000 years) and from the equatorial Pacific (over the last 410,000 years). Together with the recent Pacific carbon isotope data of Shackleton et at., [1983], these data allow us to examine the temporal the glacial ice mass) and reduction in the size of variability of the continental biomass. tropical rain forests (due to increased aridity on These data also provide information on changes the continents during the most recent glacial in deep-ocean circulation and chemical composition. maximum) transfers a sufficient quantity • carbon These aspects of the data, as well as a more enriched in 12C and reduces the average 8 •cOf the detailed discussion of the stratigraphy of the ocean. The magnitude of oceanic average 61 cores, will be presented elsewhere; in this report change has been shown to be less than originally we emphasize the aspects of the data related to estimated, however, because a reduced input of changes in the continental biomass.